1. Field of the invention
The present invention generally relates to single shot structures for generating electrical pulses, and in particular for generating pulses having a desired width.
2. Background Description
It is often necessary to produce a pulse with a given width based on an input to a single shot structure. The width is commonly controlled by discharging a capacitor C with a known current I. To first order, the time will be proportional to the C/I ratio. However, it is very difficult to accurately control the absolute value of on-chip capacitors or currents, hence there is large variability in the resultant pulse width.
In general, circuits for producing pulses of specified widths are well known in the art. However, semiconductor manufacturing processes do not permit the values of specific circuit components to be controlled precisely. One attempt to address this problem is described in U.S. Pat. No. 4,580,065 to Haque. Haque discloses a circuit fabricated as an integrated circuit and which uses analog feedback and voltage references to obtain a constant duty cycle. The Haque patent generates positive and negative voltage references on-chip having a ratio proportional to the desired duty cycle, and requires a connection to an off-chip capacitor. The disclosed circuit controls the duty cycle of a periodic pulse, not the width of a single shot event.